Gelled aqueous nitric acid compositions



United States Patent ()fiice matter Patented Jan, 2, 1968 ABSTRACT 6FTHE DESCLGSURE Aqueous nitric acid-based explosives gelled by the insitu polymerization of a mixture of monoand polyethylenicallyunsaturated polymers soluble and stable in the system.

CROSSREFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of copending application Ser. No. 504,169, filedOct. 23, 1965, now abandoned, which, in turn, is a continuationin-partof copending application Ser. No. 486,223, filed Sept. 9, 1965, nowabandoned.

DISCLOSURE Liquid nitric acid finds use in the metallurgical,fertilizer, explosive, and general chemical process industries, Where itserves principally in the preparation of inorganic nitrate salts or as anitrating or oxidizing agent. However, use of the liquid acid as achemical reactant or as an acidulating agent has always required specialprotection of both personnel and material, inasmuch as the inherentcorrosiveness normally characteristic of a strong acid is accompanied inthe case of nitric acid by particularly strong oxidizing capacity. Theseprotective considerations also apply in the case of chemical propellantsand ex plosives in which the oxidizing power of nitric acid is harnessedby reacting it under controlled conditions with one or more fuels.

The potential of liquid nitric acid as sole or principal oxidizingcomponent in such high-energy compositions apparently was first clearlyrecognized by Dr. Hermann Sprengel in the early 1870s. In a paper in1873 in the Journal of the Chemical Society (London), 26, 796-807, henoted that of all the then commonly available oxidizing agents, nitricacid contained the highest percentage of available oxygen. However,Sprengel also recognized the difficulties inherent in using the liquidacid as an oxidizing component for such charges. In British Patent 2642of 1871, in which he initially proposed explosive compositions composedof liquid oxidizing agent, specifically nitric acid, in combination withone or more liquid or solid combustible substances, i.e., fuels, apreferred method set forth for preparing such explosives was mixing ofthe oxidizer and fuel components immediately prior to use.

Since the time of sprengels initial work on this type of charge, whichoften is referred to by his name, a number of attempts have been made tointroduce modifications permitting easier and safer handling of suchcharges. For example, several variations directed particularly towarduse of more economical and, in some cases, safer fuels and towardimprovements in packaging and dispensing of the charges have beenintroduced, especially under the impetus of World Wars I and II, duringwhich charges of the Sprengel type were of increased interest formilitary use.

However, in spite of these modificaitons, explosives containing liquidnitric acid have never received widespread acceptance, either formilitary purposes or in the civil explosives market. A principal reasonfor this lack of acceptance is not difiicult to ascertain. Liquid nitricacid is harmful to man, as well as to other animal and plant life, andinjury or damage can result not only from contact with the liquid acidbut also from exposure to the fumes (nitrogen oxides) that can evolvefrom the liquid acid under some conditions. Corrosiveness of the acid tomany materials of construction likewise has been a problem, at leastuntil relatively recently, in that the imperative for reliably leak-freestorage, mixing and transfer facilities has often been associated withexcesses in weight and in costs of making and using such equipment.

A less immediately obvious, but no less significant, disadvantage ofsome of the explosives containing liquid nitric acid is theirsensitivity to detonation by impact, or high shock sensitivity. Evenwhen carefully prepared to avoid highly incompatible components andexcessive heats of mixing, certain explosives of this type also havebeen known to fume off during formulation. Following Sprengels procedureof mixing the liquid acid and fuel at the time and site of use,including mixing in the blast hole in the case of use of the charges asblasting explosives, can minimize the more serious consequences of theseproblems but simultaneously may generate new ones. For example, inloading of the charges into blast holes containing appreciable amountsof water, sealing or packaging material that is watertight and willremain so, even after several days or weeks exposure, is generallynecessary. Otherwise, ingress of water can lead not only todesensitization so that the charges cannot be detonated, but also todecomposition reactions associated with the high heat of dilution ofnitric acid in water. Even in so-called dry holes, losses of liquidcomponents through subterranean fissures or simmilar faults and reactionof the nitric acid with some minerals, e.g., carbonate-containingformations, can create problems.

Since maintenance of the liquid nitric acid and the fuel components inseparated state until the time of use has not proved entirelysatisfactory, either in terms of equipment and packaging requirements orin terms of the results achieved, other methods directed particularlytoward immobilizing and/ or dessensitizing the nitric acid-containingaxplosives have been tried. For example, certain mineral substances ofhigh absorptive capacity, such as kieselguhr and other diatomaceousearths, clays of various types and, more recently, colloidal silicas,have been proposed for use in nitric acid-containing explosives. Thesematerials tend to thicken and immobilize the liquid explosives, or theirliquid constituents, can in some cases impart a desirable reduction insensitivity to detonation by impact, and may also help to provide atleast temporary homogeneity in charges composed of nonmisciblecomponents. However, such additives are inert, or substantially so, withrespect to contributing to the total power of an explosive and hence areless than ideal constituents. Also they do not yield cohesivecompositions of a Wide range of consistencies.

More recently, a number of high-molecular-weight organic compounds,particularly certain linear polymers of the vinyl type, have been foundto swell in explosives containing liquid nitric acid and hence to imparta thickening effect. Unlike the inorganic modifiers referred to above,such organic thickeners do contribute to total explosive strength andpower. Like the inorganic agents, they also can aid in providinghomogeneity in compositions prepared from immiscible components,especially in the as-made state. However, neither of these types ofadditives is inherently capable of giving products of high viscosity,cohesiveness or flexibility. Water resistance, a desirablecharacteristic especially in explosives to be used in wet, orpotentially wet, locations, also is not markedly improved by their use.Furthermore, what thickening and stabilizing action is initiallyimparted by the linear polymer additives often is lost, in Whole or inpart, inasmuch as certain of these additives tend to undergo degradationin the presence of nitric acid.

This invention provides a simple and effective means for obtainingmodified aqueous nitric acid which is easier and safer to handle thanthat known heretofore and which has controlled free acidity andexcellent stability. These and other properties of the improved nitricacid of this invention make the products of this invention particularlysuitable as propellants, etching compositions, in chemical syntheses, asan acidifying agent in mineralogical processes, and in other uses whereaqueous nitric acid is now employed. In addition, physical propertiessuch as cohesiveness, controlled flexibility and consistency and theability to maintain dispersion of solids therein as well as theirexplosive properties make compositions of this invention, particularlythose containing conventional fuels, sensitizers, etc., outstanding andlow cost explosives adaptable, for example, for formulation in fixedplant facilities as well as mobile and other oil-site equipment.

The improvement of this invention comprises copolymerizing, in aqueousnitric acid of about from to 99%, and preferably 30 to 98% strength, amixture of monoand polyethylenically unsaturated monomers soluble andstable in the system, said mixture comprising:

(at) About from 1 to 20%, and preferably 2 to by weight based on theaqueous nitric acid (i.e., the total weight of water and acid) ofmonomer selected from at least one of the group consisting of (l)monomers having the formula:

where X is M is alkali or alkaline earth metal or an ammonium group andthe Rs are the same or different and each independently selected fromthe group consisting of hydrogen, lower alkyl, cycloalkyl, hydroxyalkyl,or cyanoalkyl radicals of 1 to 8, and preferably 1 to 4, carbon atoms,and (2) monovinyl pyridines and (b) About from 1 to 30%, and preferably2 to 10%, by weight, based on (a), of monomer polymerizable therewithhaving at least two terminal unsaturated methylene (Cl-IF) groups.

Preferably, the polyfunctional monomer (b) is selected from the groupconsisting of (l) monomers having the formula [A] Y and (2) divinylbenzenes, wherein A is selected from the Rs independently being selectedfrom the group set forth above with regard to monomer component (a) andthe same or different from the particular Rs in (a); n is 2 to 5,inclusive, and preferably 2 or 3; and Y is a bridging radical,preferably free of benzenoid unsaturation and of 3 to 20 atoms inaddition to hydrogen, to which a plurality of the unsaturated moietiesin (b) are bonded by oxygen or nitrogen atoms in Y; provided, however,that when the polyfunctional monomer component (b) consists essentiallyof at least one divinyl benzene, the monofunctional monomer (a) consistsessentially of at least one monovinylpyridine. Preferably, the aforesaidbridging radical Y consists of carbon and hydrogen atoms alone ortogether with ether oxygen linked to the indicated unsaturated moietiesthrough terminal wherein N is a member of a heterocyclic ring, theshortest chain in Y adjoining each of said moieties and including saidterminal atoms being about from 3 to 14 atoms long. The main requirementof Y is that it be stable in the system and not insolubilize (h).Compositions of this invention containing aqueous nitric acid of highstrength, particularly those over strength, preferably contain up to60%, and preferably 5 to 30% by weight, based on the aqueous nitricacid, of dissolved salt of acid having an ionization constant in waterof at least 10 The preferred explosive compositions of this inventionalso usually contain fuels, sensitizers and other additives stable inthe system including those conventionally used with Sprengel-typeexplosives. The aforementioned dissolved salts normally are dissolved inthe aqueous nitric acid prior to polymerization. Other additives,including the additives for explosives, can be incorporated in thenitric acid prior to polymerization, or particularly in the case ofadditives of marginal stability or those having an inhibiting eifect onpolymerization, incorporated in the gel products after polymerization.However, in any case, the polymerization occurs in situ, that is, in theaqueous nitric acid component of the composition.

The expression soluble in the nitric acid and similar terms, as usedherein, refer to components having appreciable solubility at ambienttemperature (2025 C.) in the particular strength of nitric acid beingemployed, i.e., a solubility of at least about 10% by weight, andpreferably appreciably greater, e.g., 50 to Furthermore, themonoethylenically unsaturated monomer should not preferentially form, inaqueous nitric acid, homopolymers which are removed, e.g., byprecipitation, from the aqueous nitric acid medium or agglomerate intofiocculates or lumps. Copolymerization forms a crosslinked structurewhich is a gel rather than a solid precipitate. This gelled structureswells in the aqueous nitric acid, holding the aqueous nitric acid, andis of substantially constant composition throughout. The gelledcrosslinked structure contains a fairly low ratio of polymer solids toliquid phase, e.g., less than about 1:5, this ratio being roughly equalto the weight ratio of the monomers to the liquid phase, in contrast toprecipitates or agglomerates in which there is a relatively high ratioof polymer solids to liquid phase.

Reference to stability in nitric acid unless otherwise indicated refersto the absence of significant degradation of the monomers, or theircopolymerization products, in the particular strength of aqueous nitricacid involved. Since prolonged stability often is of specialsignificance in the instant gelled compositions, stability in nitricacid unless otherwise specified refers particularly to the absence ofappreciable degradation in copolymer-containing samples when they aresubjected to an accelerated thermal stability test that involves heatingof the material in question in nitric acid of the specified strength ata temperature of 50 C. (122 F.) for a period of at least 8 to 12 hours.

Strength as used with reference to nitric acid expresses in percent therelationship between the weight of 100% (dry) nitric acid and the weightof nitric acid-pluswater in a particular acid. The aqueous nitric acidused in the compositions of this invention generally will have astrength of about from to 99%. Most effective utilization of the gellcompositions and their inherent properties is usually achieved, however,when the strength of the nitric acid employed is at least about 30%,particularly about from 40 to 98%, and these latter strength ranges willordinarily be preferred. As will be described more fully hereinafter,certain specific strengths, or ranges of strength, within these broadlyspecified ranges can be especially suitable for particular applicationsof the gelled nitric acid compositions, for example, in the formulationof explosives and/ or for use with particular copolymerization products.

Preferably, to effect gel formation at the lower concentrations ofmonomers and initiators and at ambient (room) temperature, theconcentration of impurities such as metallic ions, e.g., of iron,chromium and nickel, which can be attributed to metal containers used tostore the aqueous nitric acid, should not exceed about 5 p.p.m., sincethe presence of such impurities tends to inhibit polymerization. This isparticularly desirable for acids of greater than about 75 to 80%strength.

Examples of monoethylenically unsaturated monomers which can be used inthis invention are vinyl pyridines such as 4-vinylpyridine and2-methyl-S-Vinylpyridine and acrylic monomers including nitriles such asacrylonitrile, methacrylonitrile, and u-butylacrylonitrile; acids suchas acrylic acid, methacrylic acid, ot-ethyl acrylic acid and apropylacrylic acid; esters such as methyl acrylate, methyl methacrylate, ethylacrylate, n-butyl methacrylate and nhexyl acrylate; amides such asacrylamide, methacrylamide, ot-ethyl acrylamide, N-methyl acrylamide andN,N- dimethyl acrylamide; cycloalkyl substituted acrylics, e.g.,cyclohexyl methacrylate; salts such as sodium or ammonium acrylate oralkyl ammonium acrylates; hydroxyalkyl acrylates, e.g., Z-hydroxyethylacrylate or Z-hydroxypropyl acrylate; cyanoalkyl acrylics such ase-cyanoethylacrylonitrile; and mixtures of two or more of theaforementioned monomers. Acrylic and methacrylic acid and materialshydrolyzaole thereto are particularly preferred because of the low costand rapid polymerization in the process of this invention; of theseacrylics, acrylic acid, acrylonitrile and acrylamide are of optimumefficiency. Although as previously indicated lower concentrations ofmonoethylenically unsaturated monomers can be used, usually theconcentration ranges from 2 to 20% and, especially 3 to Representativepolyunsaturated monomers that can be used in this invention include oneor more of:

Other polyfunctional monomers include acrylic and methacrylic acidesters, including mixed esters of polyols such as glycerine, sorbitol,mannitol, erythritol, pentaerythritol, diethylene glycol and triethyleneglycol; cycloalkyl and hydroxyalkyl esters, e.g.,ethylenebiscyclohexylacrylate and ethylenebishydroxyethylacrylate, andcyanoalkyl acrylics such as ethylenebiscyanoethylacrylate; polyallylcompounds such as diallyl ether, diallyl adipate, diallyl maleate,diallyl ether of pentaerythritol, diallyl amine, andN,N'-diallyladipamide; compounds with mixed groups such as allylacrylate, allyl methacrylate, vinyl acrylate and vinyl methacrylate; anddivinylbenzenes, particularly divinyl benzene per se. Of theaforementioned polyfunctional monomers, those having a bridging radicalY bearing terminal ether oxygen or amido where -N is part of aheterocyclic ring) nitrogen joined by an aliphatic chain of 1 or morealkylidene radicals I l/I Where R and R are selected from hydrogen,alkyl, cycloalkyl, aryl, or aralkyl radicals are preferred because oftheir optimum stability. Of these preferred polyfunctional monomersacrylic monomers including N,N,N"-triacrylylhexahydro-s-triazine,trimethylolpropane trimethtacrylate, ethylene glycol dimethacrylate,N,N'-methylenebismethacrylamide and, especially,N,N'-methylenebisacrylamide are particularly preferred.Alkylidenebisacrylamides wherein Y comprises a bifunctional alkylidenechain comprising 4 to 12, and usually 6 to 10, carbons with terminalamido functions are preferred polyfunctionral monomers since gelledproducts produced therefrom have outstanding storage stability. Of thesehexamethylenebisacrylamide and decamethylenebisacrylamide areparticularly preferred. Divinylbenzenes .are suitable for crosslinkingthe monovinyl pyridines.

Particularly when the gelled nitric acid of this invention is to be usedas an explosive composition, the monomers employed for in situcopolymerization need not be highly purified. For example, acrylamidesand methacrylamides obtained by the hydrolysis of the correspondingnitriles in the presence of concentrated mineral acid, e.g., sulfuricacid, can be used directly without purification. Also, if desired, atleast a portion of the polyunsaturated monomer, e.g., methylenebisacrylamide, can be formed in the same crude hydrolysis mixture for example byadding an aldehyde such as formaldehyde thereto in proportionstoichiometrically necessary to yield the desired quantity ofpolyunsaturated monomer.

The choice of particular monomer components, as well as theconcentrations of these components used to prepare the gelledcompositions of the invention, both are influenced by the strength ofthe nitric acid and frequently also by the intended end-use of theresulting gelled composition. Generally speaking, the concentration ofmonomers increases with acid strength and desired gel consistency, whilethe mono and polyfunctional components are so selected that they haveroughly similar polymerization rates under the reaction conditions. Theaqueous nitric acid is converted from a liquid or water-like consistencyto a gel characterized by the presence of an aqueous acid phase and asolid phase substantially uniformly distributed or dispersed therein,The gels are substantially homogeneous down to substantially colloidaldimensions and additionally resist finite shear forces. Thus, thecopolymerization products form a continuous or semicontinuous matrix inthe gelled compositions of the invention, at least a portion of thecontinuity in this matrix structure being provided by crosslinking ofpolymer chains by the aforementioned polyethylenically unsaturatedmonomer components which, owing to their polyfunctionality, are capableof reacting at two or more sites in the molecule. The proportions ofliquid and solid phases have been found to be widely variable, so that abroad spectrum of product consistencies is readily obtainable, e.g.,soft jellies, moderately stiff or very stiff gelatin-like masses thatfrequently are resilient, elastic, and even rigid shapable products. Inaddition, as will be shown more fully hereinafter, the consistency andother physical and mechanical characteristics of the gel products ofthis invention can be changed considerably through inclusion of avariety of other dissolved and/or dispersed components, in addition tothe nitric acid and copolymer constituents. For satisfactory gelformation, the concentration of the aforedescribed monoethylenicallyunsaturated monomer or monomers used in forming the copolymerizationproducts generally will constitute at least 1% and usually about 2% ormore by weight of the aqueous nitric acid, although in a few casessomewhat lower concentrations can be effective. Higher minimumconcentrations likewise can be desirable, depending particularly on thestrength of the nitric acid, the particular monomer or monomersemployed, and the presence or absence of additional dissolved orsuspended components in the gelled compositions. On the other hand, theconcentration of the monoethylenically unsaturated monomer(s) willusually not exceed about 20% by weight of the aqueous acid, since evenwhere solubility considerations permit higher concentrations of thesematerials, the resulting gelled compositions are not materially improvedthereby.

Compared to the monoethylenically unsaturated monomers, only relativelyminor proportions of the abovedescribed polyethylenically unsaturatedmonomer components have been found necessary to form gelled productspossessing desirable consistencies and satisfactory stabilities. Aboutfrom 1 to 30% by weight of the polyunsaturated monomer, with referenceto the monoethylenically unsaturated component or components, willusually be used, although again the exact concentration will beinfluenced not only by the factors previously enumerated as affectingthe amounts of monoethylenically unsaturated monomers used but also bythe particular polyethylenically unsaturated monomer chosen. In general,the polyunsaturated monomers containing the carboxamido groups tend tobe more effective at the lower concentrations of the specified rangethan do those containing the carboxylic ester groups The particularpolyfunctional monomer used depends to some extent on the monofunctionalmonomer used. The polyfunctional monomer should polymerize sufficientlyrapidly with respect to the monofunctional monomer so that, e.g.,homopolymerization of the monofunctional monomer does not runsubstantially to completion before copolymerization begins. Thus, forexample, if a vinyl pyridine is used, the polyfunctional monomer can bea divinylbenzene, while the aforementioned monomers of formula [A] Y canbe used with a much wider spectrum of monofunctional monomers includingboth acrylics and vinyl pyridines.

At high acid strengths, particularly above it also can be desirable tohave a dissolved salt present in the aqueous nitric acid used to formthe gelled compositions of this invention. The addition of dissolvedsalt can also be desirable at acid strengths less than about 80% withthe monofunctional nitrile monomers. To provide the necessary solubilityin the nitric acid, such additive will ordinarily be chosen from saltsof acids having a first ionization constant, measured in water atapproximately 20 C., of not less than about 10*. As with the remainingcomponents of the gelled compositions, the added salts should be stablein the aqueous acid, i.e., not undergo oxidation or reduction readily.They further should not have any deleterious effects on, i.e., notmaterially inhibit, the formation of the copolymerization products. Theammonium, alkali metal, and alkaline earth metal salts of acetic,nitric, sulfuric, chloric, perchloric and phosphoric acids, includingboth neutral and acidic salts in the case of the polyfunctional acids,generally satisfy these criteria and hence constitute a particularlysuitable group of salts. Among these, the ammonium and potassium salts,e.g., NH NO KNO NH OAc, KOAc, (NH4)zSO4, NH4HSO4, K2804, Nliclos,NI'I4C104, and l-IP0 where OAc is acetate anion, have good solubilityand effectiveness over a wide range of nitric acid strengths and usuallyare preferred.

The close interrelationship of the foregoing variables can be seen moreclearly in terms of particular monomer combinations and specificstrengths of nitric acid. For example, when acrylonitrile is used as thesole monoethylenically unsaturated monomer, it is particularly effectivefor gelling nitric acid having strengths of about from 50 to 80%.Preferred concentrations of the acrylonitrile under these conditionsgenerally are about from 5 to 20% by weight of the aqueous acid,especially when em ployed in combination with about from 7 to 25% byweight, based on the acrylonitrile, of one of the previously describedpolyunsaturated monomers. However, superior gel formation, particularlyin the upper portion of the specified nitric acid strength range, i.e.,at strengths of about from 65 to 80%, can be achieved when the nitricacid contains one of the aforementioned dissolved salts, preferably in aconcentration of about from 5 to 50% by weight. At the same time, thedissolved salt permits satisfactory gel formation from lowerconcentrations of the monomers, both monoand polyunsaturated, thangenerally is possible in the absence of such salt.

On the other hand, when acrylamide is used as the sole monoethylenicallyunsaturated monomer, the strength of the nitric acid usually varies morewidely, since this monomer is capable of giving preferred gels in nitricacid having strengths of about from 5 to 99%. This amide monomergenerally will be employed in concentrations of about from 3 to 10% byweight of the aqueous nitric acid, together with about from 3 to 15% byweight, based on the acrylamide, of polyunsaturated monomer. Gelformation also is usually improved in these acrylamide-containingsystems, especially at nitric acid strengths of about 80% or above, bythe presence of dissolved salt in the nitric acid. Dissolved saltconcentrations of about from 2 to 50% by weight of the nitric acid areusually employed. Again, the salt additive has a favorable ability tolower the concentrations of monomers, both monoand polyacryllc,efiective for gel formation.

Acrylic acid, methacrylic acid, and esters of these two acids are allsimilar to acrylamide in terms of effective concentrations of themonoand polyunsaturated monomers and also in terms of salt addition.Systems containing these latter monomers find particular use in gellingnitric acid havin a strength of about from 50 to 99%.

Still further variations in component proportions and properties of thegelled products are possible through use of mixtures of at least two ofthe aforementioned monoethylenically unsaturated monomers. Acrylonitrilecan be combined with acrylamide or acrylic acid, for example. In suchmixtures, most effective utilization of the monomers and the gelledproducts and their properties generally is achieved when theacrylonitrile constitutes a maximum of about 80% by weight of the totalmonoethylenically unsaturated monomer mixture. Under these conditions,the nitric acid strength is about from 50 to 75%, the concentration ofmonoethylenically unsaturated monomer about from 4 to 15% by weight ofthe aqueous nitric acid, and the concentration of the polyunsaturatedmonomer component on the order of about from 5 to 15% by weight of thetotal monoethylenic monomers. Other combinations of monoethylenicallyunsaturated monomers found particularly effective under similarconditions in preparing the elled nitric acid compositions of thisinvention include mixtures of acrylonitrile and methacrylic acid,mixtures of acrylamide and acrylic acid, mixtures of acrylamide andmethacrylic acid, and mixtures of acrylic acid and methyl acrylate.

In addition to the aforementioned constituents, the reaction mixturesused in preparing the compositions of this invention also contain one ormore promoters or initiators which are soluble at least to the extent of0.1%, and preferably to substantially greater extent, in aqueous nitricacid and not substantially consumed or inactivated beforepolymerization, e.g., not consumed or inactivated after about 30 minutesat polymerization conditions. Promoters meeting the above criteriainclude sodium, potassium and ammonium salts of inorganic per acids suchas persulfates, perborates and pervanadates; hydrogen peroxide,particularly in combination with ferrous ion; cobaltic ion (Co+ alone orin combination with hydrazine or persulfate; and organic peroxide andazo catalysts such as azobis(isobutylnitrile),a,u-azob?s(a,'y-d-imethyly-rnethoxyvaleronitrile, tertiary butylhydrogen peroxide, methylvinyl etherhydrogen peroxide, and peraceticacid. Inorganic redox couples, combinations of reducing and oxidizingagents, are preferred. With some promoters such as the aforementionedorganic azo and peroxide catalysts as well as with the cobaltic ionalone and the ferrous ionhydrogen peroxide couple, it is preferable touse weaker acids particularly of less than 50% strength.

Redox systems that utilize a source of persulfate ion (5 as onecomponent have been found especially suitable in these respectsthroughout the range of acid strengths. The persulfate ions, which areintroduced into the nitric acid as a soluble persulfate salt, e.g., anammonium or alkali metal salt, can be used alone with the nitric acid asa redox couple to promote the copolymerization reaction.

An added reducing agent can also be used in forming the polymerizationcatalyst or promoter system. Reducing agents found to be especiallysuitable in having the required solubility, activity and stability innitric acid include certain nitrogen bases, especially hydrazine,hydroxylamine, and carbohydrazide. These reactants can be introduced asthe free bases, as hydrates, or as soluble salts of inorganic or organicacids, preferably free of halogen. Among the mentioned reducing agents,hydrazine is especially effective and is preferred, particularly whenused in combination with persulfate and copper ions. Optimum utilizationof added reducing agent is generally realized in aqueous nitric acid ofstrengths up to about to the reactants usually being less effective athigher acid strengths.

Generally higher rates of polymerization are achieved when thepolymerization system also includes a minor amount of metal ion, usuallytransition metal ion. Group 18 metal ions, especially silver and copperions, are particularly effective for this purpose. These metal ions alsoare introduced as soluble inorganic or organic salts, e.g., as thenitrates, sulfates, or acetates. (Halogen-containing salts, especiallythose containing chlorine, should generally be avoided inasmuch as theytend to retard or inhibit the copolymerization reaction.) Otherpreferred persulfate couples are H O [S O Co+ -[S O and Fe+ [S O Ingeneral, the total amount of promoters varies somewhat with theparticular promoter and monomers and increases, at least at lowconcentrations, with the desired speed of polymerization andconcentration of monomer. but usually falls within the range of aboutfrom 0.1 to 30% based on the total weight of monomers to be polymerized.The optimum concentration of the preferred persulfate ions, based ontotal monomers, both monoand polyethylenically unsaturated, can varyconsiderably, depend ing on the particular polymerization system,including the presence or absence of additional promoter components, butordinarily will be about from 0.1 to 15 weight percent of the combinedmonomers. Even higher concentrations are Without deleterious effect, butoffer no advantages in terms of polymerization rates or product quality.In general, it is preferred to employ about from 0.5 to 10% by weight ofpersulfate ions, based on the total monomers.

Silver ion, when used as a promoter, generally is effective in ratios ofabout from 0.1/1 to 5/ l, with reference to the Weight of persulfate,and weight ratios of about from 0.3/1 to 3/ 1 are usually preferred.Copper ion in combination with hydrazine on the other hand, is mostactive as a polymerization promoter at much lower ratios, viz, about0.005/1 to 0.5/1, based on persulfate ion, and preferably is employed inconcentrations providing a copper-to-persulfate ion weight ratio ofabout from 0.01/1 to 0.3/1. Relatively slow polymerizations are achievedwith silver ion as a promoter, compared to those when copper ion andhydrazine are used. Thus, considerable variation in rates of gelationcan be obtained through choice of a particular metal ion as well as itsconcentration.

The added reducing agent, when used, will generally be present in aweight ratio, based on persulfate, of about from 0.01/1 to 2/1, andpreferably from about 0.01/1 to 0.5/1.

Preparation of the gelled nitric acid compositions of this invention canbe accomplished by simple mixing of the nitric acid, optionallycontaining dissolved salt, with the monoand polyethylenicallyunsaturated monomers, followed by addition of thepolymerization-promoting component or components. In a few cases,solution of the monomers in the nitric acid can be facilitated by firstdissolving them in a small amount of water; such water is of coursetaken into consideration in determining the desired final acid strength.The mixing and polymerization steps ordinarily are conducted at ambienttemperatures (2025 C.), but temperatures down to the freezing point ofthe mixture can also be used without deleterious effects except for alower rate of reaction. Temperatures above about 40 to 50 C., on theother hand, should ordinarily be avoided during the polymerizations, inthat they tend to inhibit gelatio-n even when the resulting gelledcompositions, once formed, are capable of withstanding temperatures ator above this level. When preparing gelled compositions using lowmonomer concentrations, e.g., less than about 3% total monomer, thereaction mixture is preferably maintained at lower temperatures, e.g.,at about 1015 C.

The rate of polymerization and, in some instances, product consistencycan also be affected by the presence of nitrogen oxides and oxygen,either in dissolved form or as the gases, as well as by the presence oflarge amounts, in the monomers, of compounds conventionally used toinhibit free-radical polymerizations of the same. Compensation for thesevariations can be provided, when necessay, by increasing slightly theconcentrations of the monoers and/or of the polymerization promoters. Analternative and generally more economical procedure, however, is toreduce the concentrations of these polymerization-retarding componentsprior to the polymerization. In the case of the nitrogen oxides andoxygen, this can be accomplished by sparging the nitric acid with aninert gas, e.g., nitrogen or carbon dioxide, and then preferablymaintaining it under an inert gas atmosphere until the polymerizationreaction is complete.

The rate of gelling and the viscosity of the gelled compositions of thisinvention can be varied according to the needs of a particularapplication. In general, the rate of gelling and the viscosity of thegel can be increased by increasing the strength of the acid, byincreasing the percentage of monoethylenically unsaturated monomer inthe system, by increasing the relative proportion of thepolyethylenically unsaturated monomer used for a given quantity of themonoethylenically unsaturated monomer, and/ or by increasing, withinlimits, the quantity of polymerization promoter, such as persulfate and/or hydrazine employed in the system. The addition of a dissolved salt,typically ammonium nitrate, to the system usually increases theviscosity of the final gelled products, and, as is discussed above, isusually preferred for use in gelling nitric acid of greater than about80% strength.

The compositions of this invention have greater homogeneity, resistanceto disintegration or leaching by water, and stability, i.e., resistanceto degradation and settling out of components, than compositions whichare merely thickened. This greater homogeneity, stability andwaterresistance is particularly advantageous when the gelled nitric acidcompositions, which can contain added fuels and sensitizers, are to beused as explosives particularly in wet locations, since disintegrationand leaching of a composition by water, if such occurs, can lead tofailures to detonate or to propagate a detonation throughout the lengthof an explosive column. If the explosive structure degrades, i.e., byvirtue of disintegration of the gel structure, subsequent segregation ofcomponents, particularly undissolved (solid) fuels and sensitizers, asdiscussed hereinafter, can occur under the force of gravity, and thecomponents in a borehole, whether in a container or cartridge, shuckedtherefrom, or simply pumped into a borehole will become so heterogeneousthat complete failure of detonation or propagation of detonation throughthe entire length of the column of explosive charge will occur.

As indicated hereinbefore, the gelled nitric acid compositions can beemployed for a variety of applications in which liquid aqueous nitricacid is ordinarily employed, e.g., as an oxidizing or nitrating agent inchemical synthe sis, as an acidifying agent in mineralogical and otherprocesses, in preparing nitrate salts, and in like operations. Thegelled nitric acid compositions find particular merit in suchapplications when delayed action is desirable or required, inasmuch asthe gels tend to release the acid slowly. However, the gelled nitricacid compositions of this invention have been found to have particularutility as explosives, and as described more fully hereinafter, they arereadily formulated to meet the specific require ments of such use.

As can readily be seen from Example 97, the gelled nitric acid systemsare markedly superior to any of the thickened nitric acids proposed inthe prior art, for example, compositions thickened by polymethylmethacrylates of molecular weights within the range of 50,000 500,000,or copolymers of methylvinylether and maleic anhydride (e.g., molwt.-l.25 The compositions of this invention are characterized byviscosities Within the range of about from 100,000 to over 20 millioncps, preferably 200,000 to 5 million cps, values about 10,000

times greater than those compositions based on the thickened nitric acidheretofore known. In addition to improvement in consistency and solidsdispersion as compared with the prior art, it should be noted thecompositions of this invention can be formulated more rapidly than priorart thickened compositions since, as shown by Example 97, they do notrequire long dissolution times and, in general, particularly with thepreferred compositions, attain substantially full viscosity in a mannerof seconds or minutes. That the monomers used in this invention evenpolymerize in the highly acidic (pH l) nitric acid environment is, perse, quite unexpected. Inherent safety, though, e.g., freedom fromspilling, splashing and leaking together with reduced fuming, is anotherdistinguishing characteristic of the products of this invention.

Several of the gelled nitric acid compositions described above areinherently satisfactory as detonating explosives with further additives,i.e., they can be detonated with moderatestrength primers in diametersof 6 inches or less under moderate conditions of confinement, such asprovided by a borehole or a container of moderate wall thickness.However, preferably for explosive applications, the compositions of thisinvention also contain one or more fuels and/or non-explosivesensitizers which are compatible with (stable in) the nitric acid of thestrength used in preparing the gels. Examples of non-explosive fuels arethe monoand dinitro aromatic hydrocarbons, such as nitrobenzene,o-rnononitrotoluene and dinitrotoluene; liquid and solid hydrocarbonsand hydrocarbon fractions, particularly refined petroleum and mineraloils and the aromatic hydrocarbons, such as benzene, toluene, and thexyleues; carbohydrates, including various cellulose and starch products,e.g., cornstarch, potato starch, wood and paper pulps and sugar;siliceous fuels, including silicon itself and mixtures and alloys ofsilicon with heavy metals, e.g., ferrosilicon; and sulfur. Light metalfuels such as aluminum also are potentially useful in some of the gelledcompositions, provided that they are, or can be made, sufficientlyresistant to attack by the nitric acid. The gel copolymer per se acts asa fuel and except as otherwise indicated is included in calculating theamount of nonexplosive fuel and oxygen balance. Ordinarily, the gels foruse as explosive compositions will be formulated to have an oxygenbalance of about from 25 to +10%. Surfactants can be employed to insurecomplete dispersion of some fuels, e.g., the petroleum and mineral oils,in the explosive composition.

In addition to the non-explosive fuels and/ or sensitizers named abovethe explosive compositions of this invention can, if desired, contain anadditive of the art-recognized self-explosive type, provided that suchadditive is stable in the strengths of nitric acid used in preparing thegels. TNT, for examples, exhibits a high degree of stability in allstrengths of aqueous nitric acid and hence is a particularly usefuladditive of the self-explosive type. Examples of other self-explosivecomponents which can be used in the gelled nitric acid basedcompositions of this inventron are RDX, nitrocellulose, smokeless power,and other organic nitramines, nitrates and nitrocompounds. For reasonsof economy and compatibility, TNT is preferred for use in thecompositions of this invention. The TNT or its mixtures (e.g., withammonium or sodium nitrate) can 'be introduced into the compositions inthe form of crystals, grains, pellets, flakes, or other particulate formwhich allows ready dispersion thereof. In general, up to and preferablyup to 40%, by Weight of self-explosive additive based on weight of thecomposition is used.

In further addition to the fuels and/ or sensitizers discussed above,the explosive compositions of this invention can contain up to about85%, and preferably 5 to 50%, based on the total weight of composition,of an inorganic oxidizing salt, particularly an inorganic nitrate saltsuch as ammonium or sodium nitrate. The presence of such salt assists inthe in situ polymerization of some of the nitric acid compositions,particularly of compositions based on 13 nitric acid of greater thanabout 80% strength and, also, contributes to the explosive energy of theformulation. At least part of the salt, when used, will be dissolved inthe system; however, some of the salt can be undissolved providing thatit is uniformly distributed throughout the gelled nitric acid matrix.

Stable, gelled nitric acid compositions found especially economical andefiicient as detonating explosives comprise a uniform blend of:

(a) About from 25 to 95% by weight of aqueous nitric acid having astrength of from about 40 to 99%, and preferably 60 to 97%;

('b) About from to 30% of a non-explosive fuel, preferably selected fromsiliceous fuels, light metals, liquid and solid hydrocarbons,carbohydrates, sulfur, monoand dinitro aromatic hydrocarbons, andmixtures of such fuels and/or sensitizers;

(c) O to about 40% ticularly TNT;

(d) 0 to about 50% of an inorganic oxidizing salt, typically, aninorganic nitrate; and

(e) An in situ copolymerization product of (1) About from 1 to 20% andpreferably 2 to based on the weight of aqueous nitric acid, of at leastone monoethylenically unsaturated monomer, as defined above, whichpreferably is acrylamide, acrylonitrile, methacrylonitrile, acrylicacid, methacrylic acid, methyl acryl-ate, methacrylamide or a mixture oftwo or more of these monoethylenically unsaturated monomers of thisgroup, and

(2) About from 1 to 20% and preferably 2 to by Weight based on component(1) of a polyethylenically unsaturated monomer, which preferably isN,N-methylenebisacrylamide, N,N hexamethylenebisacrylamide,N,N-decamethylenebisacrylamide, N,N,N-triacrylhexahydro-s-triazine,trimethylolpropane trimethacrylate, or ethylene glycol dimethacrylate.

In addition to the aforementioned oxygen balance of -25 to +10%, optimumexplosive properties also have been found to be achieved when these gelscontain a maximum of about 40% by weight of water, on a totalcomposition basis.

In general, the gelled nitric acid-based blasting compositions of thisinvention are prepared by blending of the ingredients, e.g., in a rotarytype mixer such as a Lightnin AG-100 mixer, keeping in mind the samegeneral considerations for the control of the process as were discussedabove. As mentioned, it is generally preferred to sparge the nitric acidwith an inert gas such as nitrogen or carbon dioxide, e.g., for about 15minutes, before it is incorporated with other components of thecomposition and to maintain the components while being blended under aninert atmosphere until polymerization is complete. Particularly whenmaking large volume mixes, e.g., greater than about 25 to 50 lbs., it isdesirable to provide a means to remove heat of polymerization or othersecondary effects. In practice, sufii-cient cooling is usually rovidedby placing the vessel in which the components are being blended or mixedin a bath of cooling water, typically at about 15 to C., the volume ofwater surrounding the vessel being approximately at least twice thevolume of the composition to be prepared in the vessel. Alternatively,cooling can be provided by pumping coolant around the vessel. Usually,the sparged nitric acid is introduced into the cooled mixing vesselfirst and the other ingredients added individually thereto while thecontents of the vessel are being agitated. Polymerization romoters,including reductants such as hydrazine, hydroxylamine, orcarbohydrazide, are usually the last ingredients added. Agitation isusually continued until after the composition is gelled, particularlywhen the added fuels or sensitizers are sol-ids such as for example,ferrosilicon, sulfur, aluminum, silicon, or starch, which must bedistributed uniformly throughout the gel matrix. Where fuels of aself-explosive sensitizer, parid or other additives of marginalstability or additives which inhibit polymerization are to beincorporated in the compositions, all ingredients except such additivescan be mixed and gelled as previously described, then such additivesblended with the finished gel.

As indicated above, for explosive applications preferred ranges ofnitric acid strength are from about 60% (corresponding to a maximumwater content of about 40%) to 97%. In general, the unit or bulkstrength of an explosive composition based on gelled nitric acidincreases with increasing strength of the nitric acid gelled.Accordingly gels of nitric acid of strength or higher are usuallyemployed where high bulk strength is a requisite, e.g., in the bottom ofa borehole. The bulk or unit strength of an explosive composition, itsrelative ease of initiation, and its minimum critical diameter can alsobe regulated to a large degree by the type and quantity of fuel and/ orsensitizer employed. In general, a solid fuel such as ferrosilicon,sulfur or siliceous fuels is used to increase the bulk strength of acomposition. Organic nitro compounds, typically mononitrotoluene, ordinit'rotoluene or, in particular a self-explosive composition,especially TNT, are incorporated to provide compositions which areeasily initiated, e.g., by a relatively small primer or by a blastingcap, in some cases, in small diameters. In many cases, a combination offuels will be employed within the range of proportions indicated to givea composition having the desired physical and explosive propelties.

Preferred gelling systems for explosive compositions comprise as themonoethylenicaliy unsaturated monomer acrylonitrile or acrylamide,either used alone or in admixture with acrylic or methacrylic acid. Thepolyethylenically unsaturated monomer preferred isN,N'-methylenebisacrylarnide, N,N-hexarnethylenebisacrylamide, N,N'-decamethylenebisacrylamide, trimethylolpropane trimethacrylate, orethylene glycol dimcthacrylate. In addition to being readily availableat reasonable cost, these compositions are particularly effective inproviding firm cohesive gels having viscosities within the desired rangeof 100,000 to 5 million cps., high surface tension as evidenced by lackof stickiness or tackiness, ready workability, flexibility, waterresistance, and other desirable physical characteristics in the as-madestate. Further, blasting agents including these preferred gellingsystems retain their initial physical and explosive properties duringstorage after production. The preferred gelling systems also allowrelatively Wide latitude in the consistency of the explosive productmade, to fit the needs of a particular type of blasting.

The compositions of this invention can be packaged in containerscompatible with the gelled nitric acid, e.g., of polyethylene,polypropylene, or aluminum, and stored until time of use withoutdeterioration, gassing or sepa-' ration of components. Sometimes, at thetime of use the explosive compositions are stripped from theircontainers and loaded directly into the borehole. Such a shuckingoperation is possible with the non-tacky flexible gels of thisinvention. Even when freed from the container these compositions retaina high degree of resistance to disintegration and leaching by waterwhich may be present in the borehole or which may enter the boreholeafter the compositions are loaded. Alternatively, the compositions canbe prepared at the site of use and pumped or dumped directly into theborehole, which can be lined with a material such as polyethylene, whichis both water-impervious and compatible with the gelled nitric acid.When such is the case, it is usually desirable that all components ofthe composition be liquid for ease of mixing and pumping thecomposition. Usually, the compositions to be pumped will be less viscousthan those to be shocked from their containers and accordingly willcomprise somewhat less of the copolymer.

The explosive initiation system used with the gelled nitric acid-basedexplosive compositions of this invention naturally will be one which iscompatible with nitric (10% by weight of acrylamide) in the presence ofpromoter systems as indicated in Table III.

Similar results are obtained when the compositions are gelled by the insitu polymerization in nitric acid of so- TABLE III Acid ExampleStrength, Promoter Material, Percent Used Gel Product DescriptionPercent 20 (NHmS Oa, 6% of monomers Fe(NH4)z(SO4)26Hz0, Firm gel in 2sec.

10% f Sv 40 .d Firm gel formed instantaneon y.

50 do Medium firm gel in 11 sec.

30 H202, 2% of monomers FG(NH4):(SO4)z-6H2O, 30% of Medium firm gelformed instantaneously.

Finn gel in 3.5 min.

Weak gel in 8 min.

Firm gel essentially instantaneously. Fir-m gel in min.

Firm gel in 1 min.

sulfate) (NEIL/Co .005.01).

Cobaltie sulfate (hydrous) 6.2% of monomers Co, 1.512%;t of monomers(NI-1025208, 70% of cobaltic en a e.

Firm gel in 80 sec.

dium, potassium and ammonium acrylates, cyclohexyl methacrylate,a-cyanoethyl acrylonitrile, or 2-hydroxy ethylacrylate, each withN,N-methylenebisacrylamide in the general amounts and by the procedureshown above. In a like manner, similar results are also obtained whenthe promoter for the in-situ polymerization comprises perborate andpervanadate ions.

Examples 77-86 Gelled nitric acid compositions are prepared by themethod described above for Examples 1-76, each composition being gelledto a weak gel by the in situ polymerization in 70% nitric acid, ofacrylamide with the crosslinking monomer indicated in Table II, using apromoter system comprising [S O hydrazine, and Cu+ Samples of the gelsformed are stored at room temperature (nominally C.) and at 45 C. Foraccelerated test purposes gels are deliberately formed using lowconcentrations of monomer so that the decomposition characteristics ofthe gel can be determined more rapidly. The characteristics of each gelafter storage are summarized in Table II. Although the gels decompose intime, as formed they are useful for the purposes described hereinbefore.As seen from the attached table, gel life is markedly prolonged whenbisacrylamides having a long alkylidene chain, preferably of 6 to 10carbons, between the functional groups is used. Gel life can be extendedalso by using more of the polymerizable monomers, although at equivalentconcentrations the aforementioned improvement still pertains.

The following example compares in situ polymerized compositions of thisinvention with aqueous nitric acid compositions thickened withprepolymerized vinyl polymers.

Example 97 In 240 parts of nitrogen-sparged nitric acid are dissolved7.5 parts of acrylamide (3% based on the aqueous nitric acid) and 0.5part of N,N-methylenebisacrylamide. Next, promoter consisting of 0.1part of (NHQ S O 0.1 part of CuSO -5H O and 0.006 part of N H -H O areadded and mixing and polymerization continued under a nitrogen blanketat about 20 to 25 C. A firm gel is obtained in about 165 sec. After 30minutes and 24 hours, respectively, the viscosity of the gel is 500,000cps. and 400,000 cps. as measured on a Brookfield Synchro-lectricViscometer, Model RVT, with a helipath attachment using a TE spindle at5.0 r.p.m. (at 1.0 r.p.s. the viscosities are 1,400,000 and 1,100,000cps., respectively) As a comparison, attempts are made to prepare threethickened 70% aqueous nitric acid compositions by stirring 250 parts ofthe aqueous acid with 7.5 parts each of a copolymer of methyl vinylether and maleic anhydride, having a molecular weight of about 1,250,000(Gantrez AN 169), a homopolyrner of methyl methacrylate having amolecular weight of about 400,000 (Lucite 2008). The methyl vinylether-maleic anacrylate having a molecular weight of about 50,000(Lucite 2008). The methyl vinyl ether-maleic an- TABLE II Acryl- Exampleamide, Polyunsaturated Monomer, percent Storage Characteristics of GelNumber percent of Acrylarmde Temperature After Storage of HNO;

3 lllethylenebisacrylamide, 4.6 Room. Liquid in 13 days.

2 Methylenebisacrylamide, 7. do Liquid in 3 days.

2 Methylenebisacrylamide, 7.- 45 0 Liquid in 18 hr.

3 Trimethylenebisacrylamide, Room. Liquid in 14 days.

2 Trimcthylenebisaorylamide, 8 do Weak gel in 3 days.

3 Hexamethylenebisacrylamide, 6.6. do Liquid in 20 days.

2 Hexamethylenebisaerylamide, 10 do... Medium firm gel in 3 days.

2 Hexamethylenebisacrylamidc, l0 45 C Liquid in 4.5 days.

2 Decamethylenebisacrylamide, 12.5. Room. Firm gel in 3 days.

3 Decamethylenebisaerylamide, 6 45 C Liquid in 4 days.

Examples 87-96 Gelled nitric acid compositions are prepared by themethod described above for Examples l-75, each composition being gelledby the in situ polymerization in nitric acid of the strength indicatedin Table III of acrylamide (7% based on weight of aq. HNO and MBAAhydride copolymer dissolved in about 45 minutes to yield a thin syrupyliquid having a viscosity of about cps. measured as described above butusing a TA spindle at 5.0 rpm. The 400,000 mol. Wt. polymethylmcthacrylate does not dissolve even after two hours stirring. The 50,000mol. wt. polymethyl methacrylate dissolved in Examples 98 to 103 Sixexplosive compositions are prepared by in situ polymerization of theformulation summarized in Table IV, each composition being based on thegelation of 70% strength aqueous HNO by the copolymerization product ofacrylamide (AA) and N,N'-methylenebisacrylamide (MBAA) efifected in thepresence of the redox system introduced in the form of (NH S O and AgNOVarious fuels and sensitizers as shown in Table IV are incorporated inthe formulations. These compositions are prepared by the mixing andpolymerization procedures outlined above. The compositions are preparedby first thoroughly dispersing all ingredients except the promoters inthe aqueous nitric acid, then adding the promoters (8 and Ag and finallycontinuing mixing at a temperature of about 20 to 25 C. for about tominutes, during which time the polymerization runs substantially tocompletion. The nitric acid is sparged with nitrogen to remove dissolvedoxygen and nitrogen oxides and the combining of ingredients conductedunder a blanket of nitrogen to exclude atmospheric oxygen. A nitrogenblanket is maintained over the mix by bleeding nitrogen into apolyethylene bag inverted over the mix pot, the mixer shaft goingthrough the bag.

The percentages and ratios reported in the tables below are on a weightbasis; the parts of each ingredient components are reported on the basisof parts by weight of the total composition. Values for themonoethylenically unsaturated monomer, i.e., acrylamide, are given bothin terms of weight of the monomer, in terms of the total weight ofcomposition, and in terms of percent by weight of the monomer based onthe aqueous nitric acid in the 22 Examples 104 and 105 Explosivecompositions are prepared and tested as described for Examples 98 to103; however these compositions are gelled in situ by thecopolymerization of ac rylonitrile (ACRN) and N,N-methylenebisacrylamidein the presence of AgNO and (NH S O The formulations and their physicaland explosive characteristics are summarized in Table V.

10 TABLE v Example 104 105 AC RN (acrylonitrile) 9. 7 7. 0

I5 MBAA 1.1 0.8 70% HNOs. 79. 8 76. 6

gNO 0. 3 0. 3

(N H 8 0 g. 0.5 0. 4 Starch 14. 9 N itrobenzene- 8. 6 AORN, percent ofHNO; l2. 2 9.1

20 MBAA, percent of ACRN- 11 11 Velocity (m./sec.) 6, 640 3, 390Diameter (in.) 1.8 3 Density (g./cc.) 1. 3 1. 3 Oxygen Balance, percent.3. 5 0. 2 Physical Appearance 1 N, N -methylenebisacrylamide 2 Cheeselike el. 3 Firm gel.

Example 106 A firm, gelled explosive composition is prepared havlate andthe polyunsaturated monomer is again N,N'-

methylenebisacrylamide (MBAA).

TABLE VI system. Similarly, values for the polyethylenically un-Monounsaturated Monomer 3.9 saturated monomer N,Nmethylenebisacrylamideare ex- 40 Methyl acrylate 2.8 pressed both in terms of parts by weightof the total com- Acrylamlde 1.1 position and in terms of percent byweight of the poly- MBAA 0.3 unsaturated monomer based on the weight ofthe mono- 7 HNO 29.0 ethylenically unsaturated monomer. AgNO 0 .3 Thegelled formulations are loaded into 2- and 3-inch (N flz zqs diameter by15-inch long glass containers. The density Mineral 011 (Bayol F) 6.0 ofeach charge and detonation velocities are determined NH NO 50.0 byconventional means. In each case, detonation of the NaNO 10.0 charge iseffected by a 100-gram RDX pellet booster which Monounsaturatedmonomers, percent of HNO 13.4 is actuated by a conventional Du Pont E-94blasting cap. MBAA, percent of monounsaturated monomer 7.7 Theformulations and results of the tests are summarized Veloclty (m./sec.)2670 in Table IV. All of the formulations are firm or medium Oxygenbalance, percent +0.1 firm, non-tacky gels. Density 1.4

TABLE IV Example 98 99 100 101 102 103 30 71331? 11003.-. 73. 2 7s. 259. 2 79. 0 47.8 crylamide 6 5. 6 4. 5 4. 7 4. 5 A. .4 0.4 0.3 0.3 0.3 AN03 .4 0.4 0.4 0.4 0.4 (NH4)2S208..-. .1 0.1 0.1 0.1 0.1

DNT .3 20.3 Mineral 011 2 a. 5 0. 9 NT 24.4 10.0 NHlNIa 11. 2 30. ONaNOa- 10.0 S1tarch .t; f rr Nb fifi fi ilj il 7.7 7.9 5.9 9.4 5 a MEniiP 1 3. I g. 3 g 3535110, 51 756 0??? men I 6,140-6,800 3,080 3,700 4,700 5,040 Diameter,in 2 2 3 8 3 Density" 1.4 1.5 1.3 1.3 1 4 1DNT-dinitrotoluene (26 transition point). Bay0l]3-oi1, commerciallyavailable from Esso Refining C0.

Examples 107 to 109 Gelled explosive compositions are prepared by thegeneral procedure shown in Examples 98 to 103 except that in Example 107the components are mixed and immediately charged to the borehole beforegelation has proceeded to any substantial extent. The in situcopolymerization of acrylamide and N,N-methylenebisacrylamide iseifected in the presence (NH S O N H -H O, added as a solution of ca.0.5 molar concentration, and CuSO -5H O. Three different types offormulations are prepared:

TABLE VII Examples 107 l 108 l 109 Acrylamide-.. 6. 7 5. 1 5.6 MBAA..-0.3 0.3 0.2 011804.5Hz 0. 2 0.1 0. l (NH )2SzOs 0.3 0. 2 O. 3 6S 3% HNO;75. 8 51. 3 77. 4 26 diuitr0toluene.. 16. 7 13.0 5. 0 Ferr0si1icon 30.0Mineral oil (BayoP 6. 4 Starch 5. 0 N2Hl.H-,1O 0.01 0. 01 0. 03 AA,percent of HNO3. 8.8 9. 9 7. 2 MBAA, percent of AA 4 5. 0 3. 6

Remarks 1 Formulation gelled in situ in borehole. 2 Solids suspended ingel. 3 OiLs suspended in gel.

The formulations are loaded into ZVz-inch-diameter holes, 12 feet deep,in a limestone formation. The bottom of the borehole contains a primerunit comprising a plastic shell housing a /2-pound liquid explosivebooster composition comprising 28% DNT (26) and 72% I-INO (70% strength)which is actuated by a /2-pound charge of pressed TNT initiated by a No.6 blasting cap having an aluminum shell. After setting the primingcharge unit into the borehole, a 4-mil thick liner of polyethylene islowered into the borehole to contain the main explosive charge. Thehandling and loading of each charge of the types is described below.

Example 107-The ungelled mix is poured into the borehole liner andallowed to set to a loose gel. When actuated by the primer, the chargedetonates completely and effectively.

Example 108This gelled composition, which contains a high loading of aninsensitive solid fuel (ferrosilicon), is hard and cheese-like. Thecharge detonates at 5100 m./sec., with noticeably more violence than thefirst formulation.

Example 109This gelled composition is completely homogeneous and hashandling properties such that a large charge (17.4 pounds) can be loadedinto the borehole in a few (3) minutes. The charge detonates completelyat about 4980 m./sec.

Examples 110-113 Gelled explosive compositions of the formulationstabulated below are prepared and tested basically as described forExamples 98 to 103, the mixing vessels being submerged in (ice) water at1720 C. In these compositions, the gelling system is thecopolymerization product of acrylamide and N,N'-methylenebisacrylamideprepared in situ in the presence of a (NI-I -S O N H -H O added as asolution of about 0.5 molar concentration, and CuSO -5H O. As can beseen, the water content of the composition varies from about 40%, whichusually is the maximum allowable to assure reliable propagation ofdetonation by the composition in 6-inch diameter, to 1% as representedin the formulation comprising HNO of 97% strength. All compositions setup to form cohesive gels within about 3 to minutes.

TABLE VIII Example 111 112 113 97% TINO3 67.7% IINOs.

Acid Strength 97 97 56. 2 53.7 Total Water in compn 1 1 34. 5 36. 8Acrylamide, percent of HNO; 11. 8 11.5 11.0 11.1 MBAA, percent ofacrylamide 10. 5 11. 1 3. 3. 3 Detonation Velocity, m./sec 4, 310 4, 5304,880 4, 700

1 In addition to that in aq. HNOz.

Example 1 14 97% HNO 50. Acrylamide 3. MBAA 0.5 NH NO 26.05 Sulfur 20.(NI-1.9 5 0 0.4 011504, 100.00

Example 115 A mixture of crude acrylamide sulfate and crudemethylenebisacrylamide sulfate is formed in the same reaction mixture asfollows. Sulfuric acid (471 parts) is charged to a three-necked flaskand water (86.5 parts) added drop- Wise, the temperature rising to 100C. during the addition. Copper (0.2 part) is added as polymerizationinhibitor. The contents of the flask are cooled to 18 C. and 12.0 partsof a 37% formaldehyde solution (4.4 parts) added. Acrylonitrile then isadded dropwise until 246 parts is present. During this addition thetemperature of the reaction mixture rises to 45 C. After the addition ofacrylonitrile is completed, heat is applied until the temperature of thereaction mixture is C. and maintained at this temperature for 10minutes.

Eighteen (18) parts of the crude reaction product, which comprises 7.02parts acrylamide and 0.05 part methylenebisacrylamide, is then used togel parts of ntirogen sparged 75% nitric acid. The promoter consists Ofpart CIISO4'5H20, part (NH4)2S208, and 0.016 part of N H -H O andgelation is effected at 20 C. A firm gel is obtained in 4 minutes.

The crude product is also used to form explosive com- Examples 116 and117 Acrylamide. 3. 3

MBAA 0. 09 0. ()9 Crude Hydrolysis Product 1 7. 8 75% HNOi 83. 2 79. 2Hydrocarbon distillate ("Dee-Base" Oil) 10. 7 10. 2 Starch 2. 5 2. 4CuSO4.5HgO 0. 04 0. 1 (N ihssosflll 0. 20 0. 2 85% NnH4.H2O 0. 01 0. 01Gel Time (min) 9-11 9-12 Detonation Velocity at 32 F. (m./s 5, 770 2 5,640-5, 900

1 Equivalent to 3.3% acrylamide. 2 From 6 tests.

I claim:

1. A process for making gelled nitric acid which comprisescopolymerizing, in aqueous nitric acid of about from 5 to 99% strength,a mixture of monoand polyethylenically unsaturated monomers, soluble andstable in the system, said mixture comprising:

(a) about from 1 to 20% by weight, based on the aqueous nitric acid, ofmonomer selected from at least one of the group consisting of (1)monomers having the formula:

and (2) monovinyl pyridines and (b) about from 1 to 30% by weight, basedon (a), of monomer polymerizable therewith having at least two terminalunsaturated methylene groups, wherein X is selected from the groupconsisting of CN, 000R, CONR and lO-M M is alkali or alkaline-earthmetal or an ammonium group: and the Rs are independently selected fromthe group consisting of hydrogen, lower alkyl, cycloalkyl, hydroxyalkyl,and cyanoalkyl of 1 to 8 carbons.

2. A process of claim 1 wherein (b) is at least one of the groupconsisting of (1) polyethylically unsaturated monomers of the formula[A] Y and (2) divinyl benzenes, wherein the As are independentlyselected from the group consisting of o 1) (nape-(L, (ii) CHr-CHP and(iii) CHFCH- at least one A being (i) or (ii); n is 2 to 5 inclusive;and

Y is a bridging radical to which a plurality of said unsaturatedmoieties in (b) are bonded by oxygen or nitrogen in Y; provided thatwhen (b) consists essentially of (b) (2), the monofunctional monomer (a)consists essentially of (a) (2).

3. A process of claim 2 wherein the monofunctional monomer component of(a) is selected from (a) 1) and 2e polyfunctional monomer component (b)is selected from monomers of the formula 4. A process of claim 3 whereinsaid nitric acid is of least 30% strength.

5. A process of claim 4 wherein the polymerization mixture additionallycontains up to about 60% by weight, based on the aqueous nitric acid, ofsalt having a first ionization constant in water of at least 10- 6. Aprocess of claim 4 wherein the Rs bonded to the a-canbon in theunsaturated moieties in the said monomers (a) and (b) are selected fromthe group consisting of hydrogen and methyl.

7. A process of claim 6 wherein said monomer component (a) is a mixtureof acrylonitrile and acrylic acid.

8. A process of claim 6 wherein (a) is acrylamide and (b) is wherein mis 1 to 12, inclusive.

9. A process of claim 6 wherein the polymerization mixture contains aredox promoter couple.

10. A process of claim 9 wherein said promoter comprises persulfate.

11. A process of claim 10 wherein the polymerization mixtureadditionally contains at least one of the group consisting of hydrazine,hydroxylamine and carbohydrazide as auxiliary promoter.

12. A process of claim 10 wherein said polymerization mixtureadditionally contains group 1(B) metal ions.

13. A process of claim 4 for making water-bearing explosives whichcomprises adding to the reaction mixture prior to said in situpolymerization about from 5 to 30%, based on the total weight of thecomposition, of nonexplosive fuel, including monomer components (a) and(b).

14. A process of claim 13 is promoted with persulfate.

15. A process of claim 14 wherein said polymerization is additionallypromoted with at least one of the group consisting of hydrazine, Cu"-and Ag.

16. Stable gelled nitric acid comprising a mixture of about 5 to 99%strength aqueous nitric acid and in situpolymerized copolymer of (a)about from 1 to 20% by weight based on the aqueous nitric acid ofmonomer selected from at least one of the group consisting of (1)monomers having the formula:

wherein said polymerization and (2) monovinylpyridines and (b) aboutfrom 1 to 30% by weight, based on (a), of monomer polymerizabletherewith having at least two terminal unsaturated methylene groups,wherein X is selected from the group consisting of M is alkali oralkaline-earth metal or an ammonium group and the Rs are independentlyselected from the group consisting of hydrogen, lower alkyl, cycloalkyl,hydroxyalkyl and cyanoalkyl of 1 to 8 carbons.

17. A product of claim 16 wherein (b) is at least one of the groupconsisting of 1) polyethylenically unsaturated monomers of the formula[A],,Y and (2) divinyl ben- 27 zenes, wherein the As are independentlyselected from the group consisting of at least one A being (i) or (ii);11 is 2 to 5, inclusive; and Y is a bridging radical to which aplurality of said unsaturated moieties in (b) are bonded by oxygen ornitrogen in Y; provided that when (b) consists essentially of (b) (2),the monofunctional monomer (a) consists essentially of (a) (2).

18. A product of claim 17 wherein the monofunctional component (a) isselected from (a)(1) and the polyfunctional monomer component (b) isselected from monomers of the formula (oH2=( 1 )nY 19. A gelled nitricacid based composition of claim 18 which comprises up to 85% of TNT andup to 95% of aqueous nitric acid having a strength of about 40 to 99%.20. A gelled nitric acid-based composition of claim 18, said compositionbeing an explosive and comprising a uniform blend of:

(a) about from 25 to 95% by weight of aqueous nitric acid having astrength of about from 40 to 99%;

(b) about from to 30% by weight of non-explosive fuel selected from thegroup consisting of siliceous compounds, light metals, hydrocarbons,sulfur, monoand dinitro aromatic hydrocarbons, and

(c) in situ copolymerization product of (1) about from 1 to based on theweight of (a) of at least one of the group consisting of acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, acrylic acid,methacrylic acid, methyl acrylate and methyl methacrylate and (2) aboutfrom 1 to 20%, based on the Weight of (1), of at least one of the groupconsisting of N,N methylenebisacrylamide, N,N'hexamethylenebisacrylamide, N,N' decamethylenebisacrylamide, N,N',N"triacrylylhexahydro s triazine, trimethylol propane trimethacrylate andethylene glycol dimethacrylate. 21. An explosive of claim 20 40% byweight of TNT.

22. An explosive of claim 20 containing up to about by weight ofinorganic oxidizing salt.

23. An explosive of claim 20 having an oxygen balance of about from 25to +10.

24. An explosive of claim 20 wherein the in situ polymerization productis a copolymer of acrylonitrile.

25. An explosive of claim 20 wherein said copolymerization product is acopolymer of acrylamide and monomer of the formula containing up toabout No references cited.

BENJAMIN R. PADGE'IT, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,361,601 January 2, 1968 Joseph D. Chrisp It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 25, lines 66 and 67, Formula (ii) should appear as shown belowinstead of as in the patent:

column 27, lines 17 to 19, Formula (i), should appear as shown belowinstead of as in the patent:

w ll

Signed and sealed this 22nd day of April 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR., EDWARD J. BRENNER Attesting Officer Commissionerof Patents

